This invention is in the field of analog circuits. Embodiments of this invention are more specifically directed to circuits used as phase shifters and frequency mixers.
As well known in the art, the directional transmission and reception of wireless (i.e., radio) signals is commonly implemented by way of multiple antenna systems to which beam forming techniques are applied. In a general sense, beam forming is performed in the transmitting case by controlling the phase and amplitude of signals emitted from the various antennae to create a pattern of constructive and destructive interference in the wavefront of the combined signals. Conversely, the determination of directionality in received radio signals is effected by controlling the phase and amplitude in the combining of the received individual signals. Accordingly, circuits for shifting the phase of an electrical signal are necessary to carry out directional transmission and receipt.
By way of further background, many types of data communications, both wired and wireless, involve the modulation of a carrier signal with a modulating signal at a “baseband” frequency that represents the payload data being communicated. Frequency mixer circuits for accomplishing the “mixing” of the baseband signal and the carrier signal are commonly utilized in these communication systems.
FIG. 1 illustrates, in block diagram form, a generalized conventional architecture for the phase shifting or mixing of periodic signals, which in this example are orthogonal sinusoidal signals. In this simple example, oscillator 2I generates a sinusoidal signal A cos(ωRFt) at a given frequency ωRF, and oscillator 2Q generates a sinusoidal signal) A cos(ωRFt+90°) at the same frequency and amplitude as, but 90° out of phase from, the signal generated by oscillator 2I. These signals are applied to an input of amplifiers 4I, 4Q, respectively. In the general case, amplifier 4I applies a gain α(t) to the signal A cos(ωRFt) from oscillator 2I, and amplifier 4Q applies a gain β(t) to the signal A cos(ωRFt+90°) from oscillator 2Q. The amplified signals from amplifiers 4I, 4Q are applied to analog adder 5, which produces the output signal Y(t) from the sum of those two signals.
As known in the art, a phase shifter will be realized by the architecture of FIG. 1 for the case in which amplifiers 4I, 4Q apply constant (i.e., non-time-varying, or DC) gains α, β, respectively, to the orthogonal sinusoidal signals, where:∀(α,β)≦1; andα2+β2=1In other words, points representing the pair of gains α, β will all lie on the unit circle. One can thus derive the output signal Y(t) as:Y(t)=αA cos(ωRFt)+βA cos(ωRFt+90°)and thus as:Y(t)=A cos(ωRFt+φ)where:
  ϕ  =            tan              -        1              ⁡          (              β        α            )      Accordingly, the architecture of FIG. 1 generates a phase shift in the input sinusoid A cos(ωRFt) by an angle φ corresponding to the ratio of the two constant gain values.
Also as known in the art, a frequency mixer will be realized by the architecture of FIG. 1 by the application of sinusoidal gain functions α(t), β(t) by amplifiers 4I, 4Q that are at the same frequency as one another, but differing from the frequency ωRF from oscillators 2I, 2Q, and in an orthogonal relationship with one another. More specifically, for gain functions α(t), β(t):α(t)=α0 cos(ωBBt)β(t)=β0 cos(ωBBt+90°)where:∀(α0,β0)≦1; andα02+β02=1(i.e., on the unit circle), one can derive the output signal Y(t) as:Y(t)=α0A cos(ωBBt)cos(ωRFt)+β0A cos(ωBBt+90°)cos(ωRFt+90°)and thus as:Y(t)=A cos((ωRF+ωBB)t+φ)where:
  ϕ  =            tan              -        1              ⁡          (                        β          0                          α          0                    )      
As suggested by the above example, the frequencies at which phase shifters and mixers are required to operate can be quite high, well into the radio frequency (RF) bands. At these frequencies, conventional high frequency phase shifters tend to use passive components, such as quadrature hybrids, or are based on lumped elements in effecting these functions. These implementations necessarily come with significant limitations, including time-varying and unbalanced loads presented by the circuits to the high frequency oscillators, the generation and effect of noise in the transmission paths, non-linearities, and other departures from ideal performance, as well as tending to consume significant power during operation. In addition, passive components suitable for high frequency use are not necessarily well-suited for integration into single-chip solutions, and add significant cost and size to the eventual end system.